On UKVAC, I'm actually trying to get reproduction glass sets printed. I may also be able to help out here. Print onto the glass and then get a white vinyl backing applied They can't print white you see.
Here are a couple of images: -
View attachment 7297
View attachment 7300
when I made my Ramones plastics I sprayed matt white on the back of the plastic
Why not print direct to plastic(I know thats possible)then spray matt white onto the back